Variable RF attenuator

摘要

A variable pi RF attenuator includes shunt input and output branches, between which is connected a series branch. Each branch includes a voltage controlled variable impedance PIN diode. The level of a d.c. control input voltage is converted into a first d.c. current source having a magnitude proportional to an exponential function of the level. A first d.c. bias circuit supplies current of the first source as a d.c. bias for the series branch diode, while isolating the d.c. current of the first source from the diodes of the shunt branches. The control voltage is converted into a second d.c. current source having a magnitude proportional to the source voltage. A second d.c. bias circuit supplies current from the second source as d.c. biases for the diodes for both shunt branches, while isolating the d.c. current of the second source from the diode of the series branch.